Brain Pathology Case of the Month - June 2004

Rhabdoid meningioma is an uncommon meningioma variant. It has been suggested that rhabdoid meningiomas are highly aggressive tumors and that the rhabdoid phenotype represents a marker of malignant transformation in meningiomas (4). Therefore, it is classified as a variant corresponding to grade III in the recent World Health Organization (WHO) classification (3). Histologically, rhabdoid meningiomas usually exhibit signs of anaplasia, a high mitotic activity, and a markedly increased MIB-1 LI as a marker of cell proliferation. Extracranial metastases may occur in the course of the disease (4, 5). The clinical course of rhabdoid meningiomas is aggressive, with median death about three years after first appearance of the rhabdoid morphology (4). However, in one of the two larger series reported so far, four out of 15 tumors were histologically classified as benign tumors, and the clinical course was less aggressive than in tumors histologically classified as atypical or malignant ones (4). As in our case, these "benign" rhabdoid meningiomas were lacking histological features of malignancy. This raises the question if the presence of rhabdoid features is always associated with an aggressive behavior of a meningioma, and the behavior of rhabdoid meningiomas lacking other histological features of malignancy remains to be determined (3).

Another interesting feature of rhabdoid meningiomas is that in a significant number of cases, the rhabdoid cells appear only at the time of recurrence. Alternatively, as seen in our case, sometimes the rhabdoid cells may be already present in the primary meningioma, but not as the predominating histological feature (2, 4). This suggests that transformation from a focal rhabdoid phenotype to a pure rhabdoid one can occur, which is associated with a malignant behavior of the tumor in most cases reported so far.

Whether the change to the aggressive rhabdoid phenotype is associated with altered neuroradiological features of the meningioma, has not been investigated in detail. However, as seen in our case, there seems to be no marked difference in the neuroradiological appearance between rhabdoid meningioma and other common meningioma variants (1, 6).